Conventionally, in an exposure apparatus having such a positioning mechanism, if the apparatus is not to be operated for a long period of time, the exposure apparatus is turned off with the chamber being filled with nitrogen at an atmospheric pressure, so impure air will not enter the chamber from the outside. Also, when maintenance for machines in the chamber is to be performed, the chamber is filled with nitrogen, and then the chamber is partly opened to perform maintenance. In this manner, when the operation check of the wafer stage is to be performed with the chamber being filled with nitrogen or open to the atmosphere, nitrogen or dry air is used for a static pressure type bearing since exposure is not performed and in order to avoid consumption of expensive He.
With this prior art, after the operation of the wafer stage is checked, when exhausting nitrogen in the chamber to vacuum and substituting He for nitrogen to turn on the exposure apparatus, nitrogen or dry air left in the static pressure type bearing of the positioning mechanism gradually leaks into the chamber. Accordingly, it takes a long period of time for the He impurity in the exposure atmosphere in the chamber to reach a level at which exposure is possible.
The present invention has been made in view of the problem of the prior art, and has as its object to shorten a time required for the gas purity to reach a level at which exposure is possible in a positioning apparatus, atmosphere substituting method, exposure apparatus, and device manufacturing method using such a chamber, when substituting a gas in the chamber.